Z32 Looking for details on the variable power steering signals (NA).

Discussion in 'Technical' started by Veem, Oct 25, 2020.

  1. Veem

    Veem New Member

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    I've searched, but I haven't been able to find any details. Does anyone know how the variable power steering on the non-turbo z32 works?

    As far as I can tell, the gearbox speed sensor sends an AC signal to the cluster. The cluster takes that reading, and sends a conditioned signal to the power steering controller. The controller then sends a variable voltage to the power steering solenoid.

    Looking through the FSM, it suggests the cluster sends a 1-5V signal.
    '1 volt (min.) and 5 volts (max.) are alternately repeated when vehicle is driven at very low speeds.'

    That sounds to me like it might just be a 5V square wave of variable frequency. Does anyone know if that's actually the case, and if so, does the frequency map 1:1 to the AC frequency output of the speed sensor?

    Further in the FSM, it talks about the output to the solenoid.
    >0 km/h 4.4 - 6.6V
    >100 km/h 1.8 - 2.8V
    >Fail-safe 1.0 - 1.5V

    I assume these aren't actually varying voltages, but rather a PWM signal? 12v? What's the base frequency?
    The other thing is, those voltage values seem to suggest the power steering assistance isn't infinitely variable, but only has 2(3?) levels. There are a couple of graphs (steering force vs speed, and solenoid current draw vs speed) in the FSM suggesting otherwise, though.
    I don't know if those graphs are just showing the natural, nearly linear drop-off of steering force as the speed increases, or actual level of assistance the computer aims for.

    What I'd love is something like a graph or a formula of speed input frequency vs output PWM duty cycle, but I don't suppose anyone has that? Unfortunately, I don't have a scope to check this out myself, so any info on this would be helpful.


    FSM pages for reference.
    https://i.imgur.com/7Musneo.png
    https://i.imgur.com/ckBCUGb.png
     
  2. ivan129

    ivan129 Member

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    You are pretty much spot the way you have described things above. The PSC takes speed input and generates a PWM 12V pulse that control the bypass on the PS rack. I had to re-engineer my PS assist control when I stripped out the ECU and TCU and most of the wiring for an engine swap. I use an Ardunio Nano which reads a pot on a ADC input and generates a proportional PWM output to switch a DC-DC Solid State Relay. The SSR applies the PWM 12V pulses to the Rack solenoid. It just gives me one level of assist which I'm happy with.
     
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  3. jellybeans

    jellybeans Active Member

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    I thought your conversion was cool until i found out you only have 1 level of power assist.
     
  4. ivan129

    ivan129 Member

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    It does the job. I can tweak it anytime by screwing the pot which shifts the level of assist. I have too many other little tweaks on my to do list. Next thing I have in mind is a 6 speed auto. Playing around with the Holden V6 6 speed at the moment. Looking at the guts I'm pretty sure it should be able to handle my thing. Controlling the shifts wont be too hard either..
     
  5. Veem

    Veem New Member

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    Thanks for explaining that. Is there a reason you're using the SSR over a transistor? What kind of frequency are you using for the PWM? I don't suppose it matters too much, but I'm curious if the solenoid might be 'sensitive' to a particular frequency. For my purpose, I'm looking to read the speed off the CAN, and use a micro-controller to modulate the power steering assist based on that. I'm still debating if I should just feed a signal to the original (30-year-old) power steering controller, or override it completely, and modulate it using my micro.
     
  6. ivan129

    ivan129 Member

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    Don't remember what duty cycle the pulse ended up at. I just adjusted it for the best feel and comfort. I used a SSR because that's what I had in my parts box. An Solid State Relay is a transistor or fet encapsulated into a package with the driver components. One day I might spend the time to enhance it a little more however I'd like to make more time to drive it and enjoy it.
     
  7. Harleynissan

    Harleynissan AussieSpeedingFines

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    I just ran the 12v thru a cheap 5amp pwm that I mounted on the centre console, then straight to the P.S solenoid.
    Then just dial from super light to super heavy and everything in-between.
     

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